Lambda examples in C++

cpp_lambdas.cpp

#include <iostream>
#include <cstdlib>
#include <string>
#include <vector>
#include <numeric>
#include <ctime>
#include <cmath>
#include <algorithm>

std::vector<int> GenerateRandVec(int numOfNums, int min, int max);

int main() {
  std::vector<int> vecVals = GenerateRandVec(10, 1, 50);

  std::cout << "vector before sort" << std::endl;
  for(auto val: vecVals)
      std::cout << val << "\n";

  // sort a vector
  // pass in a reference to the beginning and end of our vector
  std::sort(vecVals.begin(), vecVals.end(),
  [](int x, int y){ return x < y;});

  std::cout << "vector after sort" << std::endl;
  for(auto val: vecVals)
      std::cout << val << std::endl;


  std::cout << "filter odds out" << std::endl;
  std::vector<int> evenVals;

  // filter one vector into another
  std::copy_if(vecVals.begin(), vecVals.end(),
    std::back_inserter(evenVals),
    [](int x){return (x %  2 ) == 0;});
  
  for(auto val: evenVals)
    std::cout << val << std::endl;

  // Sum vecor values 
  // Note this time we use a capture operator to enable us to use 
  // the `sum`  value inside the lambda
  std::cout << "Sum Vector Values" << std::endl;
  int sum = 0;
  std::for_each(vecVals.begin(), vecVals.end(),
    [&](int x){ return sum += x;});

  std::cout << "sum " << sum << std::endl;

  // More practise using the capture list
  int divisor; 
  std::vector<int> divVals;
  std::cout << "List divosor: ";
  std::cin >> divisor;
  std::copy_if(vecVals.begin(), vecVals.end(),
    std::back_inserter(divVals),
    [&](int x) { return (x % divisor) == 0;});

  for(auto val: divVals)
    std::cout << val << std::endl;

  return 0;
}

std::vector<int> GenerateRandVec(int numOfNums, int min, int max){
  std::vector<int> vecValues;
  srand(time(NULL));
  int i = 0, randVal = 0;
  while(i < numOfNums) {
    randVal = min + std::rand() % ((max + 1) - min);
    vecValues.push_back(randVal);
    i++;
  }

  return vecValues;
}